once.c

/*** This file is part of PulseAudio. Copyright 2006 Lennart Poettering PulseAudio is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. PulseAudio is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with PulseAudio; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.***/#ifdef HAVE_CONFIG_H#include <config.h>#endif#include <pulsecore/macro.h>#include <pulsecore/mutex.h>#include "once.h"int pa_once_begin(pa_once *control) {
pa_mutex *m;
pa_assert(control);
if (pa_atomic_load(&control->done))
return 0;
pa_atomic_inc(&control->ref);
/* Caveat: We have to make sure that the once func has completed * before returning, even if the once func is not actually * executed by us. Hence the awkward locking. */for (;;) {
if ((m = pa_atomic_ptr_load(&control->mutex))) {
/* The mutex is stored in locked state, hence let's just * wait until it is unlocked */
pa_mutex_lock(m);
pa_once_end(control);
return 0;
}
pa_assert_se(m = pa_mutex_new(FALSE, FALSE));
pa_mutex_lock(m);
if (pa_atomic_ptr_cmpxchg(&control->mutex, NULL, m))
return 1;
pa_mutex_unlock(m);
pa_mutex_free(m);
}
}
void pa_once_end(pa_once *control) {
pa_mutex *m;
pa_assert(control);
pa_atomic_store(&control->done, 1);
pa_assert_se(m = pa_atomic_ptr_load(&control->mutex));
pa_mutex_unlock(m);
if (pa_atomic_dec(&control->ref) <= 1) {
pa_assert_se(pa_atomic_ptr_cmpxchg(&control->mutex, m, NULL));
pa_mutex_free(m);
}
}
/* Not reentrant -- how could it be? */void pa_run_once(pa_once *control, pa_once_func_t func) {
pa_assert(control);
pa_assert(func);
if (pa_once_begin(control)) {
func();
pa_once_end(control);
}
}